The present apparatus is directed to a mercaptan injection mechanism and particularly one which is used with pipeline. Pipelines delivering natural gas primarily carry methane and only a few heavier molecules. Ordinarily, the gathering lines in a natural gas field deliver the flowing natural gas products to separation equipment which removes the heavier molecules such as butane or pentane. The primary constituents therefore delivered into a natural gas pipeline system are methane which is CH.sub.4, perhaps trace amounts of CO.sub.2 and perhaps some N.sub.2. This readily combustible natural gas flow is odorless. Ordinarily, the odorless natural gas is delivered by high pressure, large diameter pipelines extending hundreds of miles to local municipal distribution systems. At the local system, the odorless natural gas is provided with an odorant which is ordinarily in liquid form but which vaporizes in the flowing natural gas. This odorant is thus injected after delivery from a large diameter pipeline into a local distribution system which is then delivered through neighborhoods by small lines ultimately ending up in very small gas lines. Because the possibility of leaks increases with the number of lines and connections, most natural gas leaks occur in such populated areas so it is essential that an odorant be added in the local distribution system.
Distribution of liquid mercaptan into a high pressure line requires that the mercaptan vaporize to be distributed in the flowing natural gas. If the gas velocity is quite high, vaporization is accomplished rather easily. However, there are slack moments such as a warm day in the midst of the winter when the gas flow may actually become quite slow. Then, the liquid mercaptans which are otherwise introduced into the pipeline may form a puddle in the pipeline and not vaporize. Then when the gas flow does increase in velocity, the liquid may vaporize almost excessively for a particular flow rate of natural gas. Inevitably, this creates an irregular odorant mix in the flowing natural gas which creates problems. The odorant may be too mild in fragrance to be noticed in the event of a leak. On the other hand, the puddle may be vaporized rather quickly and create an excessively strong odorant dose, thereby creating undue alarm with just even a modest use of natural gas in an open flame. The fragrance spreads too readily if the concentration of the mercaptan in the natural gas is excessively high.
The present apparatus sets forth a mercaptan injection apparatus which particularly takes advantage of the ability of the mercaptan to vaporize in the flowing natural gas. The present apparatus is particularly able to do this by incorporating a large surface area which is exposed to the liquid mercaptan because the large area is coated in the liquid mercaptan. This enhances the delivery of the mercaptan into the natural gas by making it more easily vaporized. The large surface area boosts the vaporization process so that the mercaptans are vaporized substantially when introduced. This reduces the tendency of the newly added mercaptans to form a puddle and to otherwise retard the vaporization and distribution of the odorant material added to the natural gas.
The present apparatus is an injection mechanism which is adapted to be installed in a middle sized natural gas flow line. For instance, a very large natural gas line may deliver natural gas to a region perhaps 800 miles from the wells where the natural gas is produced. In that region, the number and size of the natural gas subscribers in the local distribution network may require a lateral line of four inches from the large transcontinental pipeline. A lateral line of four inches is typically the location at which mercaptans are then injected. It is not common to introduce the mercaptan into the large pipeline. Rather, the local distribution main is targeted for this purpose. In this instance, the local distribution line of four inches serves as a mounting for the mercaptan injection apparatus of the present disclosure. Primarily, it includes a fitting which connects with a mercaptan supply line delivering liquid mercaptan under pressure, a ball and spring in a closed cavity serially connected with a fitting which functions as a check valve which is responsive to pipeline pressure, seals and fittings connected with an elongate hollow tube, the tube being positioned axially through a threaded plug supporting internal seals for preventing leakage therearound wherein the rod extends into the pipeline. The tube defines an axial passage along the length of it and at its distal portions, the tube is perforated with a number of openings. This defines an internal cavity which is filled with wool such as metal shavings or fibrous plastic shavings. Mercaptan which is delivered through the elongate tube flows through the lower end of it and into contact with the wool particles and provides mercaptan wetting over a greater area. Perforations introduce pipeline gas flow into the cavity supported at the end of the tube. This spreads the liquid mercaptan over a much greater surface area than would otherwise occur by simple drip feeding. This enables distribution of vaporized mercaptan liquid into the flowing natural gas without creating a liquid accumulation in the pipeline .